HP Unix system file buffer issue

[jiangzx]

I have some questions about system file buffer, I manage a sybase oltp system, I use the raw device as datafile, because database application handle raw device directly, so I changed bufpages and nbuf to 0 and reduced the dbc_max_pct to a lower value than default, but after I reboot my system and found that the memory used by the file buffer is increased gradully and at last it stay in the value equal to dbc_max_pct*total physical memory and remain the same value, in my opinion, this value will increase or reduce depend on the system file buffer usages. Why?

[Bill Hassell]

As long as there is enough memory for processes and shared memory structures to remain resident (no paging) then the buffer cache will always continue to increase. Every file that is read or written (including all those used during login, or configuration) will be run through the buffer cache. The cache will shrink only when processes need more memory than is available. There is no way for the buffer cache to know which files will no longer be needed so it always grows on a busy system.

[jiangzx]

tks!